BackgroundSchizophrenia is a common severe mental disorder with complex pathogenesis. There are few studies on the correlation between kynurenine metabolites in peripheral serum and urine in schizophrenia. ObjectiveTo investigate the concentration of tryptophan-kynurenine metabolites and interleukin-6 （IL-6） in serum and urine in patients with schizophrenia， and their correlation with clinical symptoms， so as to explore potential biological characteristics related to schizophrenia. MethodsA total of 38 patients with schizophrenia who met the criteria of the Diagnostic and Statistical Manual of Mental Disorders， fifth edition （DSM-5）， and were hospitalized or attended outpatient clinic at Hangzhou Seventh People's Hospital from December 2021 to December 2022 were included in the study. Additionally， 26 healthy individuals were concurrently recruited from the community of Hangzhou to serve as a control group. All participants were requested to complete the Positive and Negative Symptom Scale （PANSS）. The levels of tryptophan （TRP）， kynurenine （KYN）， kynurenic acid （KYNA）， quinolinic acid （QUIN）， picolinic acid （PIC）， xanthurenate and 5-hydroxytryptamine （5-HT） in both serum and urine were measured using ultra-high-performance liquid chromatography-triple quadrupole linear ion trap mass spectrometry. Serum and urine IL-6 were measured using enzyme-linked immunosorbent assay. Pearson correlation analysis was conducted to examine the correlation between serum and urinary KYN metabolites， as well as the correlation between metabolite levels and clinical symptoms in the patient group. ResultsPatients with schizophrenia had significantly higher level of IL-6 in serum （U=798.500， P<0.01） and lower level of PIC in urine （U=253.000， P=0.013） compared with the control group. Additionally， level of serum KYN was positively correlated with QUIN/KYNA ratio and QUIN/PIC ratio （r=0.562， 0.438， P<0.05） in patients with schizophrenia. 5-HT/KYN ratio in serum was positively correlated with PANSS total score and negative symptom subscale score （r=0.458， 0.455， P<0.01） in patients with schizophrenia. ConclusionSerum TRP-KYN pathway metabolite levels in patients with schizophrenia were associated with neurotoxic metabolite ratios in urine and the severity of negative symptoms. ［Funded by Zhejiang Medical and Health Science and Technology Program Exploratory （number， 2022KY990）］